METHOD FOR PRODUCING AN ELECTRIC CABLE AND AN ELECTRIC CABLE

Abstract: The invention relates to a method of producing an electric cable and to an electric cable. In the invention, a short-circuiting layer is provided between an insulated conductor/insulated conductors (4a) and a protective covering (7) surrounding the conductor/s, the short-circuiting layer consisting of short-circuiting wires (3) substantially parallel with the conductor/s, and a contact member (6) positioned substantially transversely to the short-circuiting wires and connecting the wires electrically. To speed up the production process, the contact member (6) is formed of a bundle of wires.

Description: Method for producing an electric cable and an electric cable The invention relates to a method for producing an electric cable, wherein a short-circuiting layer is provided between an insulated conductor/insulated conductors and a protective covering surrounding the conductor/conductors, the short-circuiting layer comprising short-circuiting wires substantially paral- lei with the conductor/s, and a contact member posi¬ tioned substantially transversely with respect to the short-circuiting wires and connecting the wires elec¬ trically. The invention also relates to an electric cable. Power cables are provided at the production stage with a special short-circuiting layer between the insulated cable conductors and the protective outer covering. The layer consists of mutually spaced short-circuiting wires, also called neutral wires, that extend longitudinally of the cable. The layer of short-circuiting wires surrounds all of the con¬ ductors. Short-circuiting wires running in parallel with each other are connected electrically together by a contact member extending helically upon the short- circuiting wires. The contact member is often formed of metal ribbon. The purpose of the short-circuiting layer is to protect the conductors against external strains and to cause a short-circuit between the wires and the conductors if an external object, such as a spade, excavator bucket, crowbar, or another similar object penetrates through the protective covering of the cable up to the conductor for one reason or another. An example of the prior art cable structures utilizing short-circuiting wires and a contact member formed of metal ribbon is the structure disclosed in U.S. Patent 4,360,704. Another example of the prior art solutions is the solution described in Finnish Patent Application 911 600. The short-circuiting layer of the cable is usually made by stranding the short-circuiting wires and the contact member connecting them by a cage-type stranding machine around the insulated conductors of the cable, after which the protective covering is formed upon the short-circuiting wires. This way of production is, however, slow and complicated. One factor contributing to the slowness of the production process is the use of ribbon as the contact member, as ribbon material is relatively difficult to handle. Another problem with ribbon material is that it is available only in limited continuous lengths, e.g. 1,500 m, which is the maximum continuous length of usable ribbon available. Still another problem is that when the contact member is made of ribbon material, the cable has a great bending stiffness and is thus relatively difficult to handle. The poor handling properties of ribbon also causes problems upon con¬ necting the cable as the ribbon has to be revealed over a length such that the connecting point can be reached. The handling properties of ribbon material are not either the best possible in view of the connecting work itself. Moreover, ribbon material is expensive, so that its use increases the production costs. The object of the invention is to provide a method for producing an electric cable and an electric cable by means of which the drawbacks of the prior art can be avoided. This is achieved by a method according to the invention, which is characterized in that the contact member is formed of a bundle of several wires. The electric cable according to the invention is characterized in that the contact member is formed of a bundle of several wires. A major advantage of the invention is that the cable production process will be speeded up substan¬ tially as compared with the prior art technique as a bundle of wires is simple to handle as compared with ribbon material. Another advantage is that, in practice, the length of the contact member has no upper limit, as wire material is available in continuous lengths of tens of kilometres. Still another advantage of the invention is that the completed cable is considerably less stiff than a corresponding cable made by the conventional tech¬ nique. Due to the increased flexibility the cable according to the invention has excellent handling properties. The cable according to the invention is also advantageous in view of the connecting step as the wires forming the contact member are easy to twist together for completing the connection, and a bundle of wires has much better handling properties than ribbon material. One more advantage of wire material over ribbon material is its lower price. In the following the invention will be described in greater detail with reference to a preferred il¬ lustrating embodiment shown in the attached drawings, in which Figure 1 is a schematic side view of one embodi- ment of an apparatus utilizing the method according to the invention; Figure 2 is a schematic view of one embodiment of a cable produced by the method according to the invention; and Figure 3 is a schematic view of another embodi- ment of a cable produced by the method according to the invention. Figure 1 shows the principal features of a preferred embodiment of an apparatus utilizing the method according to the invention. The reference numeral 1 indicates generally the stranding apparatus, by means of which short-circuiting wires 3 from supply reels 2 are arranged around a central conductor portion 4 of a cable to be produced. The stranding apparatus 1 may be any apparatus allowing the short- circuiting wires 3 to be stranded around the conductor portion. The stranding apparatus 1 may be e.g. a cage- type stranding machine, a reverse stranding machine, etc. The stranding apparatus as such is not relevant to the invention, so its operation and structure will not be described more closely herein. In Figure 1, the reference numeral 5 indicates schematically a device by means of which a contact member 6 connecting the short-circuiting wires 3 electrically is placed upon the short-circuiting wires 3. The device 5 may be e.g. a centre strander. The structure and operation of the centre strander are well-known to one skilled in the art, so they will not be described more fully herein, but it may suffice to state that the conductor portion 4 is arranged to run through the centre of the centre strander, which twists the contact member 6 around the conductor portion 4. An essential feature of the invention is that the contact member 6 is formed of a bundle of several wires. The centre strander 5 thus twists a bundle of several wires around the conductor portion. The bundle may be formed e.g. of straight wires. It is also possible to use a bundle with a so-called vertical spooling torsion. The contact member 6 formed of a bundle of wires as described above appears clearly from Figures 2 and 3, which show two different embodiments of a cable produced by the method according to the invention. In Figures 2 and 3, the reference numeral 4a indicates insulated conductors forming the conductor portion 4. In Figures 2 and 3, the reference numeral 7 indicates a protective covering. The embodiments of Figures 2 and 3 differ from each other merely for the part of the short-circuiting wires 3, which are stranded in different ways. In both embodiments, the contact member 6 is formed of a bundle of wires stranded upon the short-circuiting wires 3. However, it is also possible that the short- circuiting wires 3 and the contact member 6 change places, i.e. the contact member 6 is placed under the short-circuiting wires. The embodiments described above are not intended to limit the invention in any way, but the invention can be modified within the scope of the claims as desired. Accordingly, it is obvious that e.g. the cable according to the invention or its details need not necessarily be such a's shown in the figures, but other solutions are possible as well. For instance, the number of the insulated conductors may, of course, be such as required in each particular case. Similar¬ ly, it is evident that the cable may comprise dif¬ ferent layers according to the requirements in each particular case. The protective covering may be formed in any suitable manner. The number of wires in the bundle is not limited to a certain number but it may vary in accordance with other factors affecting the design of the cable.

Claims: Claims: 1. Method for producing an electric cable, wherein a short-circuiting layer is provided between an insulated conductor/insulated conductors (4a) and a protective covering (7) surrounding the conductor/con¬ ductors, the short-circuiting layer comprising short- circuiting wires (3) substantially parallel with the conductor/s, and a contact member (6) positioned substantially transversely with respect to the short- circuiting wires and connecting the wires electrical¬ ly, c h a r a c t e r i z e d in that the contact member ( 6) is formed of a bundle of several wires. 2. Method according to claim 1, c h a r a c- t e r i z e d in that the bundle is stranded upon the short-circuiting wires (3) arranged around the con¬ ductor/s (4a). 3. Method according to claim 1, c h a r a c¬ t e r i z e d in that the bundle is stranded around the conductor/s (4a), and the short-circuiting wires (3) are arranged upon the contact member ( 6) formed of the bundle. 4. Electric cable comprising at least one insu¬ lated electric conductor (4a) , a protective covering (7) surrounding the conductor, and a short-circuiting layer provided between the conductor and the protect¬ ive covering, the short-circuiting layer comprising short-circuiting wires (3) substantially parallel with the conductor, and a contact member (6) positioned substantially transversely with respect to the short- circuiting wires and connecting the wires electrical¬ ly, c h a r a c t e r i z e d in that the contact member (6) is formed of a bundle of several wires. 5. Electric cable according to claim 4, c h a r- a c t e r i z e d in that the bundle is arranged upon the short-circuiting wires (3) . 6. Electric cable according to claim 4, c h a r¬ a c t e r i z e d in that the bundle is placed under the short-circuiting wires (3 ) .

Inventors: HAGELBERG TORSTEN, HARTIKAINEN JUKKA, KAAKKO EERO, KORHONEN PERTTI, LUOMA PEKKA, MAKINEN HANNU, SAARINEN SEPPO, TANNER EERO, HAGELBERG, TORSTEN, HARTIKAINEN, JUKKA, KAAKKO, EERO, KORHONEN, PERTTI, LUOMA, PEKKA, MAEKINEN, HANNU, SAARINEN, SEPPO, TANNER, EERO
Applicants: HAGELBERG TORSTEN, HARTIKAINEN JUKKA, KAAKKO EERO, KORHONEN PERTTI, LUOMA PEKKA, MAEKINEN HANNU, NOKIA KAAPELI OY, SAARINEN SEPPO, TANNER EERO, HAGELBERG, TORSTEN, HARTIKAINEN, JUKKA, KAAKKO, EERO, KORHONEN, PERTTI, LUOMA, PEKKA, MAEKINEN, HANNU, SAARINEN, SEPPO, TANNER, EERO
Application year: 1994
Main classification: H01B9
IPC codes: H01B7, H01B9, H01B13